Acting U.S. Defense Secretary Patrick Shanahan made his second trip to the U.S.-Mexico border on Saturday as the Pentagon looks to develop a longer-term plan to support President Donald Trump's immigration policies.

Shanahan traveled to McAllen, Texas, to meet with officials and visit a migrant processing facility and Border Patrol station, two days after the White House announced Trump's intention to nominate the former Boeing executive as defense secretary.

Trump has been eager to have the military play a larger role on the border.

There are currently about 4,500 U.S. service members on the border, and they are authorized to be there until through September.On Friday, the Pentagon said Shanahan approved the transfer of $1.5 billion to build more than 80 miles of barriers on the border, part of a patchwork project after Trump failed to secure funding from Congress for a complete border wall.

Lawmakers have hinted they may respond by putting new restrictions on the Pentagon's authority to move money around.